This one is both great as well as tricky. Hopefully a million blacklists won’t get created. Then again if a blacklist only has one person or two on it, does it matter? Most likely not.
Still like the thought of getting a bit more decentralized with this. We shall see how it unfolds.
Also glad it’s not too difficult for you folks on a coding side.
From a performance perspective, there wouldn't be any big impact if many people create blacklists. It's similar to follows and mutes, both of which are maintained as similar lists. I considered using mute lists as blacklists, but decided they were semantically different enough to maintain them as separate lists.